Efficiency of Bradford‐Reactive Protein Extraction From Agriculture Soil in Relation to Soil Parameters

Abstract

The aim of the study was to investigate the hypothesis that by altering extraction time, temperature in the autoclave, and type of extractant during extraction, the maximum possible Bradford‐reactive soil protein yield could be significantly increased, and to determine the effect of so‐called color correction in such altered conditions. Another objective was to review the relation between the alternative protein pools and selected quantitative soil parameters, such as the content of soil organic carbon or total soil nitrogen. Bradford‐reactive soil protein is operationally defined by the Bradford assay to measure its concentration in a water solution, extracted under specific conditions such as high temperature in an autoclave and high ionic strength of the extractant solution. The study examined the possibility of maximum extractability by altering the temperature and the type of extractant and the relation to the color correction. We also tried to test the hypothesis whether the loads of repeated cycles could be minimized by color correction, but without prove at tested 9 cycles of extraction. The results showed that the proposed one cycle method with pyrophosphate solution and 135°C extracted 2–3 times the protein extracted by one cycle of autoclaving under the conventional condition of 121°C with a 0.05‐M sodium citrate solution. Unlike other conditions, the values from the proposed one cycle method significantly correlated with soil organic carbon content ( p < 0.05, r 2 = 0.9) and while a statistically significant correlation with the content of water stable aggregates with p < 0.05 was not found, the values of the correlation coefficient were regularly higher in combination of higher temperatures (121°C–135°C) with the strongest type of extractant (0.1‐M sodium pyrophosphate) than the rest of the combinations. The color correction factor changed the measured value of Bradford‐reactive soil protein from the proposed maximal yield variant by 11%–13% in comparison to 14%–17% under one cycle conventional condition. These findings support the possibility of reducing the number of extraction cycles in the autoclave to lower units and thus increasing practicality and efficiency of measurement. On the other hand, it may be still recommended to include color correction during measurement protocol, especially in case of datasets with substantially different soil type for example, grassland versus arable land, cambisol versus chernozem, since the influence of color correction on measured Bradford‐reactive soil protein between soils greatly differs.